High-strength and high-toughness high-magnesium aluminum alloy and preparation method thereof

ABSTRACT

The present invention relates to a high-strength and high-toughness high-magnesium aluminum alloy and a preparation method thereof. The high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises the following components in percentage by mass: 5.54-6.80% of Mg, 0.50-0.60% of Mn, 0.12-0.16% of Zr, 0.30-0.36% of Er, less than or equal to 0.3% of Si, less than or equal to 0.2% of Fe and the balance of Al. In the present invention, the content of each element is strictly controlled, after a proper amount of Zr and Er rare earth elements in mass percent are added into the aluminum alloy, the mass percent of Mg element in the aluminum alloy is further controlled, so that the Mg element can interact with the rare earth elements efficiently, and the strength and toughness matching of the aluminum alloy with an Al—Mg—Mn—Zr—Er multi-element system can be improved.

TECHNICAL FIELD

The present invention relates to the technical field of aluminum alloy, and specifically relates to a high-strength and high-toughness high-magnesium aluminum alloy and a preparation method thereof.

BACKGROUND

Aluminum alloy is a kind of medium strength alloy. It has excellent properties far better than steel, but its low strength restricts its application to a large extent. Al—Mg series aluminum alloy is a typical aluminum alloy and its main alloy element is Mg element. Mg mainly exists in solid solution and β phase (Mg₂Al₃ or Mg₅Al₈), which can obviously improve the performance of aluminum alloy through solid solution strengthening and second phase strengthening. When the magnesium content is increased to 3.5% or more, the β phase may precipitate along the grain boundaries or sub-grain boundaries; and when the β phase preferentially precipitates at the grain boundaries, a continuous network is formed at the grain boundaries of the Al-rich solid solution, which further impedes the dislocation movement.

With the magnesium content increasing, the strength of the Al—Mg aluminum alloy increases and the toughness and plasticity decrease. Most Al—Mg aluminum alloy for industrial use have Mg content of less than 5.5%. When the Mg content is less than 5.5%, the welding crack tendency of aluminum alloy decreases with the increase of the magnesium content; and when the Mg content is more than 5.5%, the aluminum alloy containing Mg is very fragile, and the welding crack tendency thereof also increases with the increase of the magnesium content, and therefore it is generally useless.

Moreover, since the Al—Mg aluminum alloy doesn't belong to the heat-treatable aluminum alloy, the performance of the Al—Mg alloy is generally further improved by hardening or microalloying. Er is a very ideal microalloying element, and the strengthening mechanism of Er in the aluminum alloy is very similar to that of Sc in the aluminum alloy. Adding Er element into pure aluminum and Al—Mg alloy can obviously refine the size of the as-cast grains and form Al₃Er nanoparticles in the alloy. The effects of pinning the sub-grain boundaries and blocking dislocation movement can be realized during alloy deformation, thereby improving the strength of alloy. When Er and Zr are added in a proper ratio, more excellent performances would be generated. However, in the prior art, even if precious microalloy elements, Er and Zr, are added into the aluminum alloy, the Al—Mg aluminum alloy still has the technical problem of low strength and toughness matching degree. When rare earth elements Er and Zr are added into an aluminum alloy system of Al—3˜5 Mg—0.5˜0.6 Mn to form an aluminum alloy with a multi-element system of Al—3˜5 Mg—0.5˜0.6 Mn—Er—Zr, the tensile strength is only 200 MPa, the yield strength is only 130 MPa, the elongation rate is only 12%, and the strength and toughness matching degree is low.

SUMMARY

In view of this, the present invention aims to provide a high-strength and high-toughness high-magnesium aluminum alloy and a preparation method thereof. When the mass percent of Mg in the aluminum alloy provided by the present invention is 5.54˜6.80%, the plasticity and the strength and toughness matching degree of the aluminum alloy are both improved significantly under the condition of maintaining the strength.

To overcome the above technical issues, the present invention provides the following technical solutions:

The present invention provides a high-strength and high-toughness high-magnesium aluminum alloy which comprises the following components in percentage by mass: 5.54˜6.80% of Mg, 0.50˜0.60% of Mn, 0.12˜0.16% of Zr, 0.30˜0.36% of Er, less than or equal to 0.3% of Si, less than or equal to 0.2% of Fe and the balance of Al.

Preferably, the high-strength and high-toughness high-magnesium aluminum alloy comprises the following components in percentage by mass: 5.70% of Mg, 0.56% of Mn, 0.14% of Zr, 0.30% of Er, 0.23% of Si, 0.16% of Fe and the balance of Al.

The present invention provides a method for preparing the high-strength and high-toughness high-magnesium aluminum alloy in the above technical solution, which comprises the steps of:

Smelting an aluminum source, a magnesium source, a manganese source, a zirconium source and an erbium source to obtain a smelted aluminum alloy liquid;

Refining the smelted aluminum alloy liquid to obtain refined aluminum alloy liquid;

Casting the refined aluminum alloy liquid to obtain an as-cast aluminum alloy;

Carrying out homogenizing annealing treatment on the as-cast aluminum alloy to obtain the high-strength and high-toughness high-magnesium aluminum alloy;

The homogenizing annealing treatment comprises the steps of: preserving heat at 310-330° C. for 20-22 h, and then preserving heat at 440-460° C. for 18-20 h.

Preferably, the smelting comprises the steps of:

Adding the aluminum source and the manganese source into a first covering agent at a first temperature for a first heat preservation to obtain an initial aluminum alloy liquid;

Adding the initial aluminum alloy liquid, the zirconium source and the erbium source into a second covering agent at a second temperature for a second heat preservation to obtain a transitional aluminum alloy liquid;

Adding the transitional aluminum alloy liquid and the magnesium source into a third covering agent at a third temperature for a third heat preservation to obtain the smelted aluminum alloy liquid.

Preferably, the refining comprises the step of:

Adding the smelted aluminum alloy liquid into a refining agent at a fourth temperature for a fourth heat preservation to obtain the refined aluminum alloy liquid.

Preferably, the casting comprises the step of:

Pouring the refined aluminum alloy liquid after a fifth heat preservation at a fifth temperature to obtain the as-cast aluminum alloy.

Preferably, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.

Preferably, the first covering agent, the second covering agent and the third covering agent are independently a mixture of CaF₂, MgCl₂ and MgF₂ or a mixture of CaF₂, MgCl₂ and CaCl₂; the adding amounts of the first covering agent, the second covering agent and the third covering agent are independently 0.3˜0.4% of the aluminum source by mass.

Preferably, the refining agent is C₂Cl₆, the adding amount of the refining agent is 0.3˜0.4% of the aluminum source by mass.

Preferably, the casting mold is used after being coated with paint, and the paint is ZnO, Na₂SiO₃ and H₂O at a mass ratio of 2:1:7.

Compared with the prior art, the present invention has the following technical effects:

The high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises the following components in percentage by mass: 5.54˜6.80% of Mg, 0.50˜0.60% of Mn, 0.12˜0.16% of Zr, 0.30˜0.36% of Er, less than or equal to 0.3% of Si, less than or equal to 0.2% of Fe and the balance of Al. In the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention, the content of each element is strictly controlled, after a proper amount of Zr and Er rare earth elements in mass percent are added into the aluminum alloy, the mass percent of Mg element in the aluminum alloy is further controlled, so that the Mg element can interact with the rare earth elements efficiently. In the aluminum alloy structure, the Mg element is fully dissolved in the aluminum matrix, realizing the solid solution strengthening effect. Furthermore, an Al₃(Zr_(x)Er_(1−x)) particle phase of L1₂ structure is formed, which is mainly composed of Al, Er and Zr. The particle phase has a size of 5-20 nm, and is uniformly dispersed in the Al matrix, presenting a certain coherent relationship with the matrix. Since the structure of the Al₃(Zr_(x)Er_(1−x)) particle phase is a cubic crystal system, belonging to the Pm3m space group, so the particle phase has the characteristics of high melting point and strong stability, which can obviously improve the strength and toughness of the aluminum alloy with an Al—Mg—Mn—Zr—Er multi-element system. When the Mg content of the high-strength and high-toughness aluminum alloy provided by the present invention is 5.54-6.80%, the comprehensive mechanical property of the aluminum alloy is obviously improved compared with the prior art. And when the Mg content of the aluminum alloy is 5.54-6.80%, the tensile strength is 255.4˜261.5 MPa, the yield strength is 140.6˜165.4 MPa, the elongation rate is 12.5˜17.6%, and the strength and toughness matching degree is high.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a TEM image of a precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in Embodiment 1;

FIG. 2 is a TEM image of the high resolution structure of the precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in Embodiment 1;

FIG. 3 is a TEM image of a precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in Embodiment 2;

FIG. 4 is a TEM image of the high resolution structure of the precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in Embodiment 2.

DESCRIPTION OF THE EMBODIMENTS

The present invention provides a high-strength and high-toughness high-magnesium aluminum alloy which comprises the following components in percentage by mass: 5.54˜6.80% of Mg, 0.50˜0.60% of Mn, 0.12˜0.16% of Zr, 0.30˜0.36% of Er, less than or equal to 0.3% of Si, less than or equal to 0.2% of Fe and the balance of Al.

By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises 5.54˜6.80% of Mg, more preferably 5.64˜5.80%, and even more preferably 5.70%. By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises 0.50˜0.60% of Mn, more preferably 0.52˜0.58%, and even more preferably 0.56%.

By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises 0.12˜0.16% of Zr, more preferably 0.13˜0.15%, and even more preferably 0.14%.

By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises 0.30˜0.36% of Er, more preferably 0.30˜0.32%, and even more preferably 0.30%.

By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises less than or equal to 0.3% of Si, and even more preferably 0.23%.

By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises less than or equal to 0.2% of Fe, and even more preferably 0.16%.

By mass percentage, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises the balance of Al.

In the present invention, Si and Fe are impurity elements in the high-strength and high-toughness high-magnesium aluminum alloy, which are inevitably existed in the preparation process of the high-strength and high-toughness high-magnesium aluminum alloy. In the present invention, the Si may form a strengthening phase of Mg₂Si with Mg, which is helpful for improving the strength performance of the high-magnesium aluminum alloy. The Fe has adverse effects on the performances of the high-magnesium aluminum alloy.

In the present invention, after a proper amount of Zr and Er rare earth elements in mass percent are added into the aluminum alloy, the mass percent of Mg element in the aluminum alloy is further controlled, so that the Mg element can interact with the rare earth elements efficiently, and an Al₃(Zr_(x)Er_(1−x)) particle phase of L1₂ structure is formed in the aluminum alloy structure, which is mainly composed of Al, Er and Zr. The particle phase has a size of 5-20 nm, and is uniformly dispersed in the Al matrix, presenting a certain coherent relationship with the matrix. Since the structure of the Al₃(Zr_(x)Er_(1−x)) particle phase is a cubic crystal system, belonging to the Pm3m space group, so the particle phase has the characteristics of high melting point and strong stability, which can obviously improve the strength and toughness of the aluminum alloy with an Al—Mg—Mn—Zr—Er multi-element system, and the strength and toughness matching degree is high.

The present invention further provides a method for preparing the high-strength and high-toughness high-magnesium aluminum alloy described in the above technical solution, which comprises the steps of:

Smelting an aluminum source, a magnesium source, a manganese source, a zirconium source and an erbium source to obtain a smelted aluminum alloy liquid;

Refining the smelted aluminum alloy liquid to obtain refined aluminum alloy liquid;

Casting the refined aluminum alloy liquid to obtain an as-cast aluminum alloy;

Carrying out homogenizing annealing treatment on the as-cast aluminum alloy to obtain the high-strength and high-toughness high-magnesium aluminum alloy;

The homogenizing annealing treatment comprises the steps of: preserving heat at 310-330° C. for 20-22 h, and then preserving heat at 440-460° C. for 18-20 h.

The aluminum source, the magnesium source, the manganese source, the zirconium source and the erbium source are not particularly limited in the present invention, and the alloy raw materials well known to those skilled in the art are used to obtain the aluminum alloy containing the target components. In the invention, the aluminum source and the magnesium source employ 99.99% of industrial pure aluminum and pure magnesium respectively, and the manganese source, the zirconium source and the erbium source employ Al—10% Mn master alloy, Al—10% Zr master alloy and Al—6% Er master alloy respectively. In the present invention, the aluminum source or the magnesium source contains a small amount of Fe and Si.

In the present invention, the smelting preferably comprises the steps of:

Adding the aluminum source and the manganese source into a first covering agent at a first temperature for a first heat preservation to obtain an initial aluminum alloy liquid;

Adding the initial aluminum alloy liquid, the zirconium source and the erbium source into a second covering agent at a second temperature for a second heat preservation to obtain a transitional aluminum alloy liquid;

Adding the transitional aluminum alloy liquid and the magnesium source into a third covering agent at a third temperature for a third heat preservation to obtain the smelted aluminum alloy liquid.

In the present invention, the aluminum source and the manganese source are added into the first covering agent at the first temperature for the first heat preservation to obtain the initial aluminum alloy liquid; the first temperature is preferably 720˜760° C., more preferably 735˜745° C., and the first heat preservation time is preferably 15˜20 min, more preferably 16.5˜17 min. In the present invention, during the first heat preservation, the initial aluminum alloy liquid is stirred, so that the internal temperature and the components of the melt are more uniform. The present invention has no special requirement for the stirring mode, and any mechanical stirring well known to those skilled in the art can be adopted.

After the initial aluminum alloy liquid is obtained, the initial aluminum alloy liquid, the zirconium source and the erbium source are added into the second covering agent at the second temperature for the second heat preservation to obtain the transitional aluminum alloy liquid; In the present invention, the second temperature is preferably 760˜770° C., more preferably 765˜768° C.; the second heat preservation time is preferably 30˜35 min; more preferably 32˜34 min.

After the transitional aluminum alloy liquid is obtained, the transitional aluminum alloy liquid and the magnesium source are added into the third covering agent at the third temperature for the third heat preservation to obtain the smelted aluminum alloy liquid; in the present invention, the third temperature is preferably 700˜710° C., and the third heat preservation time is preferably 25˜35 min.

In the present invention, the first covering agent, the second covering agent and the third covering agent in the smelting are preferably a mixture of CaF₂, MgCl₂ and MgF₂ or a mixture of CaF₂, MgCl₂ and CaCl₂, independently; when the first covering agent, the second covering agent and the third covering agent are preferably a mixture of CaF₂, MgCl₂ and MgF₂ independently, the mass ratio of CaF₂, MgCl₂ and MgF₂ is preferably 12:71:17; when the first covering agent, the second covering agent and the third covering agent are preferably a mixture of CaF₂, MgCl₂ and CaCl₂ independently, the mass ratio of CaF₂, MgCl₂ and CaCl₂ is preferably 12:71:17. In the present invention, the adding amount of the first covering agent, the second covering agent and the third covering agent are independently 0.3˜0.4% of the aluminum source by mass, more preferably 0.32˜0.38%.

In the present invention, after the smelted aluminum alloy liquid is obtained, the smelted aluminum alloy liquid is refined to obtain the refined aluminum alloy liquid.

In the present invention, the refining preferably comprises the step of:

Adding the smelted aluminum alloy liquid into the refining agent at the fourth temperature for the fourth heat preservation to obtain the refined aluminum alloy liquid.

In the present invention, the fourth temperature is preferably 760˜770° C., the fourth heat preservation time is preferably 5-10 min, the refining agent is preferably C₂Cl₆, and the adding amount of the refining agent is preferably 0.3-0.4% of the aluminum source by mass, more preferably 0.32-0.38%.

The present invention has no special requirement for the smelting and refining equipment, and any smelting and refining equipment well known to those skilled in the art can be adopted. In the embodiments of the present invention, smelting and refining are preferably carried out by employing a medium frequency induction resistance furnace.

After the refined aluminum alloy liquid is obtained, the refined aluminum alloy liquid is casted to obtain the as-cast aluminum alloy.

In the present invention, the casting preferably comprises the step of:

Pouring the refined aluminum alloy liquid after a fifth heat preservation at a fifth temperature to obtain the as-cast aluminum alloy.

In the present invention, the fifth temperature is preferably 710˜720° C., the fifth heat preservation time is preferably 20˜25 min. In the present invention, the casting mold is used preferably after being coated with paint, and the paint is preferably ZnO, Na₂SiO₃ and H₂O at a mass ratio of 2:1:7.

In the present invention, the refined alloy fluid is poured preferably when the mold is preheated to 200˜220° C., and the mold is removed after the cast ingot is cooled to room temperature. In the present invention, the size of the mold is preferably Φ65×180 mm, and the size of cast rod is preferably Φ27×175 mm. The present invention has no special requirement for the specific pouring mode, and any pouring mode well known to those skilled in the art can be adopted.

In the present invention, after the refined aluminum alloy liquid is subjected to the fifth heat preservation at the fifth temperature, the refined aluminum alloy liquid is preferably further subjected to slagging-off treatment and then poured. The slagging-off treatment can remove impurity components in the refined aluminum alloy liquid. The invention has no special requirement on the operation process of the slagging-off treatment, and any slagging-off treatment well known to those skilled in the art can be adopted.

After the as-cast aluminum alloy is obtained, the as-cast aluminum alloy is subjected to the homogenizing annealing treatment to obtain the high-strength and high-toughness high-magnesium aluminum alloy;

The homogenizing annealing treatment comprises: preserving heat at 310-330° C. for 20-22 h, and then preserving heat at 440-460° C. for 18-20 h.

In the present invention, the homogenizing annealing treatment is preferably carried out by using SX2-10-12 box-type resistance furnace, (temperature control accuracy is ±5° C.). In the present invention, the process of the homogenizing annealing treatment is preferably: preserving heat at 310-330° C. for 20-22 h, and then preserving heat at 440-460° C. for 18-20 h. The present invention has no special requirement for the specific implementation of homogenizing annealing treatment by using the SX2-10-12 box-type resistance furnace, and any implementation mode well known to those skilled in the art can be adopted.

In the present invention, the homogenizing annealing process is employed to further make full use of the interaction between rare earth elements and Mg element in the aluminum alloy with an Al—Mg—Mn—Zr—Er multi-element system, which is beneficial to improving the strength and toughness of the aluminum alloy. Before homogenizing annealing treatment, Er and Mg elements are seriously segregated and often “accompanied with segregation”, and the Er mainly exists in the form of Al(Er_(x)Mg_(1−x)) coarse composite phase; by controlling the process conditions of the two-stage homogenizing annealing treatment, nanoscale Al₃(Zr_(x)Er_(1−x)) particles are precipitated in the alloy, which form a substantially complete coherent relationship with the matrix Al and are uniformly distributed in the Al matrix, so that the alloy has the best matching between tensile strength (strength index) and elongation rate (toughness index). In addition, the present invention can obviously improve the yield strength and micro-hardness of the alloy on the basis of ensuring the tensile strength and the elongation rate of the alloy through homogenizing annealing treatment.

After the homogenizing annealing treatment, the obtained aluminum alloy is preferably cooled to room temperature in air to obtain the high-strength and high-toughness high-magnesium aluminum alloy. The present invention has no special requirement for the specific implementation of air cooling to room temperature, and any implementation mode well known to those skilled in the art can be adopted.

To further illustrate the present invention, the high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention and a preparation method thereof will be described in detail below accompany with the following embodiments, which should not be considered as the limitation to the protection scope of the invention.

Embodiment 1

1. The prepared high-magnesium aluminum alloy comprises the following components in percentage by mass: Mg 5.54%, Mn 0.50%, Zr 0.12%, Er: 0.36%, Si: 0.23%, Fe: 0.16%, and the balance of Al;

2. The preparation steps are as below:

(1) Preparation of raw materials: the matrix element Al is added in the form of an aluminum ingot with the purity of 99.9%, Mg is added in the form of a magnesium ingot with the purity of 99.9%, Mn is added in the form of Al—10% Mn master alloy, Zr is added in the form of Al—10% Zr master alloy, and Er is added in the form of Al—6% Er master alloy.

(2) Smelting, Refining and Casting of the Alloy

A medium frequency induction resistance furnace is adopted for smelting and refining The aluminum ingot and Al—10% Mn master alloy are added into the furnace for smelting at a smelting temperature of 720° C. After the aluminum ingot and Al—10% Mn master alloy are softened and collapsed, a covering agent is added for protection. The covering agent comprises the following components in percentage by weight: CaF₂ 12%, MgCl₂ 71%, MgF₂ 17%, and the dosage of the covering agent is 0.3% of the aluminum ingot by mass. The heat preservation is performed for 35 min to obtain initial aluminum alloy liquid. During the heat preservation, the initial aluminum alloy liquid is stirred so that the internal temperature and the components of the melt are uniform. When the initial aluminum alloy liquid is heated to 760° C., Al—10% Zr and Al—6% Er master alloy are added and melted, a covering agent (as above) is then added and then heat preservation is performed for 30 min to obtain transitional aluminum alloy liquid. The transitional aluminum alloy liquid is then cooled to 710° C., into which is added the magnesium ingot. When the magnesium ingot is completely melted, a covering agent (as above) is added and then heat preservation is performed for 35 min to obtain smelted aluminum alloy liquid. The obtained smelted aluminum alloy liquid is heated to 760° C., into which is added the C₂Cl₆ refining agent for refining and degas sed. The dosage of the C₂Cl₆refining agent is 0.3% of the aluminum ingot by mass. Refined aluminum alloy liquid is thus obtained and then cooled to 710° C., heat preservation is performed for 25 min and then slagging-off is carried out, ready for casting. The mold is installed and the inner surface of the mold is painted. The mold is preheated to 220° C. for pouring, and removed after the casting ingots are cooled to room temperature to obtain the as-cast aluminum alloy, wherein the size of the mold is Φ65×180 mm, and the size of the as-cast aluminum alloy cast rod is Φ27×175 mm.

(3) Homogenizing Annealing

The obtained as-cast aluminum alloy cast rod is subjected to homogenizing annealing treatment in a resistance furnace, the processes of annealing is as below: heat preservation at 320° C. for 20 h, then heat preservation at 450° C. for 20 h, and finally cooling to room temperature in air to obtain the high-strength and high-toughness high-magnesium aluminum alloy.

FIG. 1 is a TEM image of a precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in this embodiment; and FIG. 2 is a TEM image of the high resolution structure of the precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in this embodiment. As can be seen from FIG. 1 and FIG. 2, when the content of Mg element is 5.54% by mass, upon homogenizing annealing treatment, many circular phase particles with the size of 10-20 nm are precipitated in the aluminum alloy structure. It is demonstrated through EDS component analysis that the particle phase mainly consists of Al, Er and Zr elements, which is an Al₃(Zr_(x)Er_(1−x)) phase with a L1₂ structure, distributed in the Al matrix uniformly, and presents a certain coherent relationship with the matrix. The particle structure is a cubic crystal system, belonging to the Pm3m space group, so the particles have the characteristics of high melting point and strong stability.

Embodiment 2

1. The prepared high-magnesium aluminum alloy comprises the following components in percentage by mass: Mg 5.70%, Mn 0.56%, Zr 0.14%, Er: 0.30%, Si: 0.23%, Fe: 0.16%, and the balance of Al;

2. The Preparation Steps are as Below:

(1) Preparation of raw materials: the matrix element Al is added in the form of an aluminum ingot with the purity of 99.9%, Mg is added in the form of a magnesium ingot with the purity of 99.9%, Mn is added in the form of Al—10% Mn master alloy, Zr is added in the form of Al—10% Zr master alloy, and Er is added in the form of Al—6% Er master alloy.

(2) Smelting, Refining and Casting of the Alloy

A medium frequency induction resistance furnace is adopted for smelting and refining The aluminum ingot and Al—10% Mn master alloy are added into the furnace for smelting at a smelting temperature of 760° C. After the aluminum ingot and Al—10% Mn master alloy are softened and collapsed, a covering agent is added for protection. The covering agent comprises the following components in percentage by weight: CaF₂ 12%, MgCl₂ 71%, CaCl₂ 17%, and the dosage of the covering agent is 0.4% of the aluminum ingot by mass. The heat preservation is performed for 30 min to obtain initial aluminum alloy liquid. During the heat preservation, the initial aluminum alloy liquid is stirred so that the internal temperature and the components of the melt are uniform. When the initial aluminum alloy liquid is heated to 760° C., Al—10% Zr and Al—6% Er master alloy are added and melted, a covering agent (as above) is then added and then heat preservation is performed for 30 min to obtain transitional aluminum alloy liquid. The transitional aluminum alloy liquid is then cooled to 700° C., into which is added the magnesium ingot. When the magnesium ingot is completely melted, a covering agent (as above) is added and then heat preservation is performed for 35 min to obtain smelted aluminum alloy liquid. The obtained smelted aluminum alloy liquid is heated to 760° C., into which is added the C₂Cl₆ refining agent for refining and degas sed. The dosage of the C₂Cl₆refining agent is 0.3% of the aluminum ingot by mass. Refined aluminum alloy liquid is thus obtained and then cooled to 710° C., heat preservation is performed for 25 min and then slagging-off is carried out, ready for casting. The mold is installed and the inner surface of the mold is painted. The mold is preheated to 220° C. for pouring, and removed after the casting ingots are cooled to room temperature to obtain the as-cast aluminum alloy, wherein the size of the mold is Φ65×180 mm, and the size of the as-cast aluminum alloy cast rod is Φ27×175 mm.

(3) Homogenizing Annealing

The obtained as-cast aluminum alloy cast rod is subjected to homogenizing annealing treatment in a resistance furnace, the processes of annealing is as below: heat preservation at 330° C. for 20 h, then heat preservation at 440° C. for 20 h, and finally cooling to room temperature in air to obtain the high-strength and high-toughness high-magnesium aluminum alloy.

FIG. 3 is a TEM image of a precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in this embodiment; and FIG. 4 is a TEM image of the high resolution structure of the precipitated phase of the high-strength and high-toughness high-magnesium aluminum alloy product prepared in this embodiment. As can be seen from FIG. 3, when the content of Mg element is 5.70% by mass, upon homogenizing annealing treatment, there are also Al₃(Zr_(x)Er_(1−x)) nanoparticles with the size of 5˜20 nm precipitated in the aluminum alloy structure. It is known from comparison with the TEM image of Embodiment 1 that, in the structure of the aluminum alloy product prepared in this embodiment, the number of Al₃(Zr_(x)Er_(1−x)) particles increases obviously, and they are arranged in chains and distributed in the Al matrix. FIG. 4 shows the high-resolution TEM image of nanoparticles in FIG. 3, from which it is obvious that the particles are almost in a complete coherent relationship with the Al matrix, and the mechanical performance of the alloy is improved significantly.

Embodiment 3

1. The prepared high-magnesium aluminum alloy comprises the following components in percentage by mass: Mg 6.80%, Mn 0.50%, Zr 0.16%, Er: 0.30%, Si: 0.23%, Fe: 0.16%, and the balance of Al;

2. The Preparation Steps are as Below:

Steps (1) and (2) are the same as in Embodiment 1.

(3) Homogenizing Annealing

The obtained as-cast aluminum alloy cast rod is subjected to homogenizing annealing treatment in a resistance furnace, the processes of annealing is as below: heat preservation at 310° C. for 20 h, then heat preservation at 460° C. for 20 h, and finally cooling to room temperature in air to obtain the high-strength and high-toughness high-magnesium aluminum alloy.

Comparative Embodiment 1

Raw materials are formulated as in Embodiment 1, without the homogenizing annealing treatment during the preparation to obtain the aluminum alloy.

Comparative Embodiment 2

Raw materials are formulated as in Embodiment 3, without the homogenizing annealing treatment during the preparation to obtain the aluminum alloy.

Comparative Embodiment 3

Aluminum alloy is prepared as in Embodiment 1, with the difference in that the aluminum alloy comprises the following components in percentage by mass: Mg 3.91%, Mn 0.60%, Zr 0.14%, Er: 0.30%, Si: 0.23%, Fe 0.16% and the balance of Al.

Comparative Embodiment 4

Aluminum alloy is prepared as in Embodiment 1, with the difference in that the aluminum alloy comprises the following components in percentage by mass: Mg 4.52%, Mn 0.56%, Zr 0.16%, Er: 0.30%, Si: 0.23%, Fe 0.16% and the balance of Al.

Comparative Embodiment 5

Aluminum alloy is prepared as in Embodiment 2, with the difference in that the aluminum alloy comprises the following components in percentage by mass: Mg 5.15%, Mn 0.50%, Zr 0.16%, Er: 0.30%, Si: 0.23%, Fe 0.16% and the balance of Al.

Comparative Embodiment 6

Aluminum alloy is prepared as in Embodiment 2, with the difference in that the aluminum alloy comprises the following components in percentage by mass: Mg 8.00%, Mn 0.50%, Zr 0.16%, Er: 0.30%, Si: 0.23%, Fe 0.16% and the balance of Al.

Comparative Embodiment 7

Aluminum alloy is prepared as in Embodiment 2, with the difference in that the aluminum alloy comprises the following components in percentage by mass: Mg 9.28%, Mn 0.50%, Zr 0.16%, Er: 0.30%, Si: 0.23%, Fe 0.16% and the balance of Al.

Test Embodiment 1

The high-strength and high-toughness high-magnesium aluminum alloy prepared in Embodiments 1 to 3 and the aluminum alloy prepared in comparative embodiments 1 to 7 are subjected to tensile property test by adopting an Instron 8801 type material testing system. Tensile samples are prepared according to the gauge length calibration method in GBT16865-2013 Samples and Methods for Tensile Test of Wrought Aluminum, Magnesium and Alloy Products Thereof, wherein the gauge length is 25 mm, the tensile rate is 2 mm/min. An HV-1000 hardness tester is used to determine Vickers hardness, with a load of 500 g for 15 s. The results of the tensile property test are shown in Table 1 below.

TABLE 1 Mechanical properties of the high-strength and high-toughness high- magnesium aluminum alloy prepared in Embodiments 1 to 3 and the aluminum alloy prepared in comparative embodiments 1 to 7 Properties Tensile Yield Elongation Vickers Mg Strength Strength Rate Hardness Content (MPa) (MPa) (%) (HV) No. 5.54% 261.5 165.4 14.48 82.02 Embodiment 1 5.70% 275.2 202.8 17.6 82.8 Embodiment 2 6.80% 255.4 140.6 12.5 84.58 Embodiment 3 5.54% 217.4 160.42 10.35 76.7 Comparative Embodiment 1 (without homogenizing annealing treatment) 6.80% 227.25 170 8.75 84.94 Comparative Embodiment 2 (without homogenizing annealing treatment) 3.91% 180.5 110 11.2 71.32 Comparative Embodiment 3 4.52% 200.4 130.5 12.4 79.58 Comparative Embodiment 4 5.15% 231.4 159.5 13 81.46 Comparative Embodiment 5 8.00% 245.5 127.7 8.4 89.7 Comparative Embodiment 6 9.28% 200.0 100.2 6.5 96.14 Comparative Embodiment 7

As can be seen from Table 1, after adding a specific amount of rare earth elements Zr and Er, the high-strength and high-toughness high-magnesium aluminum alloy prepared in Embodiments 1 to 3 of the present invention is subjected to the homogenizing annealing treatment while controlling the mass percentage of Mg element to be 5.54% to 6.80%, so as to obtain excellent strength indexes (including tensile strength, yield strength, and Vickers hardness) and toughness index (elongation rate). However, for the aluminum alloy prepared in comparative embodiments 3˜7, after adding a specific amount of rare earth elements Zr and Er, when the mass percentage of Mg element is not controlled within the range of 5.54%˜6.80%, higher strength indexes and elongation index cannot be achieved simultaneously for the alloy obtained under the same conditions (the same smelting method and annealing process), that is, a good matching between strength and toughness cannot be achieved.

It can be seen from the above embodiments that, the content of each element is strictly controlled, and the homogenizing annealing treatment process is employed at the same time to improve the strength and toughness properties of the aluminum alloy.

The foregoing is merely a preferred implementation of the invention and is not intended to limit the invention in any manner. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be construed as the protection scope of the present invention. 

What is claimed is:
 1. A high-strength and high-toughness high-magnesium aluminum alloy, comprising the following components in percentage by mass: 5.54˜6.80% of Mg, 0.50˜0.60% of Mn, 0.12˜0.16% of Zr, 0.30˜0.36% of Er, less than or equal to 0.3% of Si, less than or equal to 0.2% of Fe and the balance of Al.
 2. The high-strength and high-toughness high-magnesium aluminum alloy according to claim 1, comprising the following components in percentage by mass: 5.70% of Mg, 0.56% of Mn, 0.14% of Zr, 0.30% of Er, 0.23% of Si, 0.16% of Fe and the balance of Al.
 3. A method for preparing the high-strength and high-toughness high-magnesium aluminum alloy according to claim 1, comprising the steps of: Smelting an aluminum source, a magnesium source, a manganese source, a zirconium source and an erbium source to obtain a smelted aluminum alloy liquid; Refining the smelted aluminum alloy liquid to obtain refined aluminum alloy liquid; Casting the refined aluminum alloy liquid to obtain an as-cast aluminum alloy; Carrying out homogenizing annealing treatment on the as-cast aluminum alloy to obtain the high-strength and high-toughness high-magnesium aluminum alloy; The homogenizing annealing treatment comprises the steps of: preserving heat at 310-330° C. for 20-22 h, and then preserving heat at 440-460° C. for 18-20 h.
 4. A method for preparing the high-strength and high-toughness high-magnesium aluminum alloy according to claim 2, comprising the steps of: Smelting an aluminum source, a magnesium source, a manganese source, a zirconium source and an erbium source to obtain a smelted aluminum alloy liquid; Refining the smelted aluminum alloy liquid to obtain refined aluminum alloy liquid; Casting the refined aluminum alloy liquid to obtain an as-cast aluminum alloy; Carrying out homogenizing annealing treatment on the as-cast aluminum alloy to obtain the high-strength and high-toughness high-magnesium aluminum alloy; The homogenizing annealing treatment comprises the steps of: preserving heat at 310-330° C. for 20-22 h, and then preserving heat at 440-460° C. for 18-20 h.
 5. The preparation method according to claim 3, wherein the smelting comprises the steps of: Adding the aluminum source and the manganese source into a first covering agent at a first temperature for a first heat preservation to obtain an initial aluminum alloy liquid; Adding the initial aluminum alloy liquid, the zirconium source and the erbium source into a second covering agent at a second temperature for a second heat preservation to obtain a transitional aluminum alloy liquid; Adding the transitional aluminum alloy liquid and the magnesium source into a third covering agent at a third temperature for a third heat preservation to obtain the smelted aluminum alloy liquid.
 6. The preparation method according to claim 4, wherein the smelting comprises the steps of: Adding the aluminum source and the manganese source into a first covering agent at a first temperature for a first heat preservation to obtain an initial aluminum alloy liquid; Adding the initial aluminum alloy liquid, the zirconium source and the erbium source into a second covering agent at a second temperature for a second heat preservation to obtain a transitional aluminum alloy liquid; Adding the transitional aluminum alloy liquid and the magnesium source into a third covering agent at a third temperature for a third heat preservation to obtain the smelted aluminum alloy liquid.
 7. The preparation method according to claim 3, wherein the refining comprises the step of: Adding the smelted aluminum alloy liquid into a refining agent at a fourth temperature for a fourth heat preservation to obtain the refined aluminum alloy liquid.
 8. The preparation method according to claim 4, wherein the refining comprises the step of: Adding the smelted aluminum alloy liquid into a refining agent at a fourth temperature for a fourth heat preservation to obtain the refined aluminum alloy liquid.
 9. The preparation method according to claim 3, wherein the casting comprises the step of: Pouring the refined aluminum alloy liquid after a fifth heat preservation at a fifth temperature to obtain the as-cast aluminum alloy.
 10. The preparation method according to claim 4, wherein the casting comprises the step of: Pouring the refined aluminum alloy liquid after a fifth heat preservation at a fifth temperature to obtain the as-cast aluminum alloy.
 11. The preparation method according to claim 5, wherein, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.
 12. The preparation method according to claim 6, wherein, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.
 13. The preparation method according to claim 7, wherein, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.
 14. The preparation method according to claim 8, wherein, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.
 15. The preparation method according to claim 9, wherein, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.
 16. The preparation method according to claim 10, wherein, the first temperature is 720˜760° C., the first heat preservation time is 15˜20 min; the second temperature is 760˜770° C., the second heat preservation time is 30˜35 min; the third temperature is 700˜710° C., the third heat preservation time is 25˜35 min; the fourth temperature is 760˜770° C., the fourth heat preservation time is 5˜10 min; the fifth temperature is 710˜720° C., the fifth heat preservation time is 20˜25 min.
 17. The preparation method according to claim 5, wherein the first covering agent, the second covering agent and the third covering agent are independently a mixture of CaF₂, MgCl₂ and MgF₂ or a mixture of CaF₂, MgCl₂ and CaCl₂; the adding amounts of the first covering agent, the second covering agent and the third covering agent are independently 0.3˜0.4% of the aluminum source by mass.
 18. The preparation method according to claim 7, wherein, the refining agent is C₂Cl₆, the adding amount of the refining agent is 0.3˜0.4% of the aluminum source by mass.
 19. The preparation method according to claim 3, wherein, the casting mold is used after being coated with paint, and the paint is ZnO, Na₂SiO₃ and H₂O at a mass ratio of 2:1:7.
 20. The preparation method according to claim 9, wherein, the casting mold is used after being coated with paint, and the paint is ZnO, Na₂SiO₃ and H₂O at a mass ratio of 2:1:7. 